The AT500 requires both batteries to be installed. Running it with only one battery — or hot-swapping down to one battery while in use — shuts down the sensor.

How to tell if a battery is missing

If the Tracker light is solid red after boot-up, the unit most likely does not have both batteries installed and the tracker will not connect to the radio

What to do

Power the unit off, insert both batteries, then power it back on.

Do not hot-swap a battery while the AT500 is running. Removing a battery mid-session — even briefly — will drop the unit to one battery and shut the sensor down.